This is a prospective study of patients receiving radiotherapy or chemoradiotherapy for anal cancer. Treatment effect in terms of survival and local recurrence will be analyzed. The utility of PET-CT and MRI for radiotherapy and for prediction of treatment effect will be investigated. Molecular and genetic markers in tumor and blood will be analyzed for prognostic and predictive effects. Patient-reported outcomes, such as faecal incontinence, sexual dysfunction and quality of life will be assessed. A structured intervention program for management of late effects will be evaluated. Symptom relief of palliative radiotherapy will be investigated. The main purpose of the study is to increase the knowledge of anal cancer treatment, improve treatment results, and improve anal cancer survivor care.